CN111965856A - Electro-optical crystal film, preparation method thereof and electro-optical modulator - Google Patents
Electro-optical crystal film, preparation method thereof and electro-optical modulator Download PDFInfo
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- CN111965856A CN111965856A CN202010865004.1A CN202010865004A CN111965856A CN 111965856 A CN111965856 A CN 111965856A CN 202010865004 A CN202010865004 A CN 202010865004A CN 111965856 A CN111965856 A CN 111965856A
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/13—Integrated optical circuits characterised by the manufacturing method
- G02B6/136—Integrated optical circuits characterised by the manufacturing method by etching
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0305—Constructional arrangements
- G02F1/0311—Structural association of optical elements, e.g. lenses, polarizers, phase plates, with the crystal
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12133—Functions
- G02B2006/12142—Modulator
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- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Optical Integrated Circuits (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
The application provides an electro-optical crystal film, a preparation method thereof and an electro-optical modulator, wherein the electro-optical crystal film sequentially comprises from bottom to top: the silicon substrate layer, the silicon dioxide layer, the silicon waveguide layer, the cladding isolation layer and the functional thin film layer; the refractive index of the coating isolation layer is lower than that of the functional thin film layer, and the coating isolation layer is subjected to planarization treatment and can be bonded with the functional thin film layer. According to the application, the coating isolation layer is adopted to replace an adhesive layer in the prior art, on one hand, the coating isolation layer can be subjected to planarization treatment, so that the surface roughness of one side close to the functional thin film layer is reduced, the diffuse reflection can be reduced, and the optical transmission loss is reduced; on the other hand, the coating isolation layer and the functional thin film layer are combined in a bonding mode, and the uniformity and the integrity of the functional thin film layer are guaranteed.
Description
Technical Field
The application relates to the technical field of semiconductor preparation, in particular to an electro-optical crystal film, a preparation method thereof and an electro-optical modulator.
Background
The silicon-based electro-optical modulator is an important component of a transceiver in an optical communication and optical interconnection system, and is a precondition for completing the conversion from an electric signal to an optical signal and realizing the transmission and processing of high-speed information on an optoelectronic integrated chip.
Silicon-based electro-optic modulators are typically integrated from electro-optic crystal films, and thus the preparation of electro-optic crystal films is of great significance to silicon-based electro-optic modulators. At present, the electro-optic crystal film is generally prepared by the following processes: firstly, preparing a silicon oxide film layer above a silicon crystal substrate layer by adopting an oxidation process, and finishing the growth of silicon crystals above the silicon oxide film layer to form a silicon waveguide layer; then, in order to bond the silicon waveguide layer and the lithium niobate thin film layer, an adhesive layer is provided between the silicon waveguide layer and the lithium niobate thin film layer. In the application of the electro-optic crystal film prepared by the process, a part of an optical signal is transmitted in a silicon waveguide layer by a silicon waveguide optical path, and a part of an optical field is modulated in the lithium niobate thin film layer to complete the conversion from an electrical signal to the optical signal.
The adhesive layer is usually coated on the surface of the silicon waveguide layer by using BCB (Benzocyclobutene) resin in a spin coating or spray coating manner, and then bonded to the lithium niobate thin film layer. After the bonding is completed, the roughness of the BCB resin surface is usually several tens of nanometers or more. However, when an optical signal is transmitted through the silicon waveguide layer and the lithium niobate thin film layer, since the surface of the BCB resin close to the lithium niobate thin film layer has a large roughness, the optical signal forms diffuse reflection on the surface of the adhesive layer during transmission, which reduces the light intensity in a required direction and causes a large optical transmission loss.
Disclosure of Invention
The application provides an electro-optical crystal film, a preparation method thereof and an electro-optical modulator, which aim to solve the problem that the light transmission loss is large due to the fact that BCB resin is used as an adhesive layer in the prior art.
The first aspect of the application provides an electro-optic crystal film, the electro-optic crystal film from the bottom up includes in proper order: the silicon substrate layer, the silicon dioxide layer, the silicon waveguide layer, the cladding isolation layer and the functional thin film layer; the silicon waveguide layer is embedded in the cladding isolation layer;
the refractive index of the coating isolation layer is lower than that of the functional thin film layer, and the coating isolation layer is subjected to planarization treatment and can be bonded with the functional thin film layer.
Optionally, the functional thin film layer is selected from one of lithium niobate, lithium tantalate, KTP and RTP, and the thickness of the functional thin film layer is 50-3000nm or 400nm-100 μm.
Optionally, the coating isolation layer is silicon dioxide or silicon nitride, the flatness of the coating isolation layer is less than 1nm, and the roughness of the coating isolation layer is less than 0.5 nm;
the coating isolation layer consists of a first coating isolation layer and a second coating isolation layer;
the first coating isolation layer is positioned above the silicon waveguide layer and has the thickness of 20nm-2000 nm; the second coating isolation layer is arranged in the silicon waveguide layer and is flush with the silicon waveguide layer, and the thickness of the second coating isolation layer is equal to that of the silicon waveguide;
the first coating isolation layer and the second coating isolation layer are integrally formed.
Optionally, the silicon waveguide layer has a ridge-shaped stripe structure, and the ridge-shaped waveguide in the silicon waveguide layer has a width of 50nm to 50 μm and a thickness of 50nm to 50 μm.
Optionally, the optical waveguide further comprises a silicon connection layer, wherein the silicon connection layer is located between the silicon dioxide layer and the silicon waveguide layer; the sum of the thicknesses of the silicon connecting layer and the silicon waveguide layer is 50nm-50 mu m, and the thickness of the silicon dioxide layer is 50nm-5 mu m.
In a second aspect of the present application, there is provided an electro-optic modulator comprising the electro-optic crystal film according to any one of the first aspect.
In a third aspect of the present application, there is provided a method for preparing an electro-optic crystal thin film, comprising:
preparing a silicon-on-insulator structure, and etching the top silicon of the silicon-on-insulator structure to form a silicon waveguide layer; the silicon-on-insulator structure sequentially comprises a silicon substrate layer, a silicon dioxide layer and top silicon from bottom to top; forming a groove structure in the silicon waveguide layer after etching;
filling a coating isolation layer in the groove structure, and flattening the coating isolation layer;
and preparing a functional thin film layer with a target thickness on the coating isolation layer to obtain the electro-optic crystal thin film.
Optionally, etching the top silicon of the silicon-on-insulator structure includes: etching the top silicon layer by a dry etching method to form a ridge-shaped strip-shaped silicon waveguide; wherein the top layer silicon is completely etched or partially etched.
Alternatively to this, the first and second parts may,
filling a coating isolation layer in the groove structure, and carrying out planarization treatment on the coating isolation layer, wherein the planarization treatment comprises the following steps:
filling a coating isolation layer in the groove structure, filling the groove structure with the coating isolation layer, covering the silicon waveguide layer, and polishing the coating isolation layer, wherein the step is repeated for at least three times;
and finally, the coating isolation layer with the target thickness is reserved above the silicon waveguide layer through polishing, the roughness of the coating isolation layer is less than 0.5nm, and the surface flatness is less than 1 nm.
Optionally, the method for preparing the cladding isolation layer on the silicon waveguide layer includes: deposition, magnetron sputtering, evaporation or electroplating.
Optionally, a functional thin film layer is prepared on the coating isolation layer by using an ion implantation method and a bonding separation method, or by using a bonding method and a grinding and polishing method.
In a fourth aspect of the present application, an electro-optical modulator is provided, which includes the electro-optical crystal thin film prepared by the preparation method provided in any one of the possible implementation manners of the third aspect.
According to the electro-optic crystal film, the coating isolation layer is adopted to replace an adhesive layer in the prior art, on one hand, the coating isolation layer can be subjected to planarization treatment, so that the surface roughness of one side close to the functional film layer is reduced, diffuse reflection can be reduced, and light transmission loss is reduced; on the other hand, the coating isolation layer and the functional thin film layer are combined in a bonding mode, and the uniformity and the integrity of the functional thin film layer are guaranteed. Furthermore, the silicon-on-insulator (SOI) wafer is used as a base material, the three-layer structure of the silicon substrate layer, the silicon dioxide layer and the silicon waveguide layer can be obtained only by etching the top silicon on the surface of the SOI wafer, and in the prior art, the silicon crystal substrate layer is used as the base material, and the three-layer structure of the silicon crystal substrate layer, the silicon oxide film layer and the silicon waveguide layer can be obtained only by continuously preparing the two-layer structure on the silicon crystal substrate layer, so that the process is simpler and more convenient.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of an electro-optic crystal film according to an embodiment of the present disclosure;
FIG. 2 is a schematic structural diagram of another electro-optic crystal film provided in an embodiment of the present application;
FIG. 3 is a schematic illustration of a planarized isolation layer of the present application;
FIG. 4 is a schematic structural diagram of a method for manufacturing an electro-optic crystal film according to an embodiment of the present disclosure;
FIG. 5 is a schematic flow chart of a method for manufacturing an electro-optic crystal film according to an embodiment of the present disclosure.
Wherein, 100-top silicon; 110-a silicon substrate layer; 120-a silicon dioxide layer; 130-a silicon waveguide layer; 140-a wrapped isolation layer, 1401-a first wrapped isolation layer, 1402-a second wrapped isolation layer; 150-a functional film layer; 160-silicon connection layer.
Detailed Description
The technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
As described in the background of the present application, in the prior art, a silicon material and a lithium niobate crystal are bonded by using an adhesive, but the adhesive used in the prior art is benzocyclobutene resin, but the benzocyclobutene resin as the adhesive is easy to generate bubbles during the curing process of bonding lithium niobate and silicon material, and particularly, the problem is more obvious when large-size (4inch and above) lithium niobate and silicon material are bonded, in addition, the usage temperature of the benzocyclobutene resin is usually lower than 400 ℃, and may fail above this temperature, and the damage recovery of lithium niobate and the like by ion implantation usually requires a temperature of 400 ℃ or above, so the preparation of a lithium niobate single crystal film with a thickness of several hundred nanometers by the benzocyclobutene resin bonding method is also limited. Furthermore, benzocyclobutene resin belongs to high polymers, and can not be flattened by using a conventional chemical mechanical polishing process, so that silicon materials and lithium niobate crystals can not be tightly attached, and the performance of the electro-optical modulator is influenced.
According to the method, the SOI wafer structure is directly adopted for preparation, and only the surface of the SOI wafer needs to be etched, so that the three-layer structure of the silicon waveguide layer, the silicon dioxide layer and the silicon substrate layer which are sequentially stacked can be obtained, and therefore, the process adopted by the embodiment of the method is simpler, more convenient and more easily obtained.
Fig. 1 is a schematic structural diagram of an electro-optic crystal film according to an embodiment of the present disclosure. As shown in fig. 1, the electro-optic crystal film sequentially comprises, from bottom to top: a silicon substrate layer 110, a silicon dioxide layer 120, a silicon waveguide layer 130, a cladding isolation layer 140, and a functional thin film layer 150. The silicon waveguide layer 130 is embedded in a cladding spacer layer 140.
The functional thin film layer 150 may be an electro-optic crystal such as lithium niobate, lithium tantalate, rubidium titanyl phosphate, or potassium titanyl phosphate.
The refractive index of the cladding isolation layer 140 is lower than that of the functional thin film layer 150, and the cladding isolation layer 140 is planarized and may be bonded to the functional thin film layer 150.
The thickness of the coating isolation layer 140 is controllable, and after planarization treatment, the surface of the coating isolation layer can be smoother, the thickness uniformity is good, so that optical signals can be well coupled between the functional thin film layer 150 and the silicon waveguide layer 130 after the electro-optical modulator is prepared, the electro-optical performance of the electro-optical crystal thin film is improved, the consistency is good, and the finally prepared electro-optical modulator is wide in bandwidth, low in loss and good in device consistency.
In addition, the material of the cladding isolation layer 140 is selected to have a refractive index lower than that of the material of the functional thin film layer 150, and the refractive index difference between the functional thin film layer 150 and the cladding isolation layer 140 can better reduce the loss of the optical signal
The silicon waveguide layer 130 prepared in the embodiment of the present application includes a plurality of ridge stripe waveguides continuously and uniformly distributed, and the silicon waveguide layer 130 is used for transmitting optical signals. In one implementation, the ridge stripe waveguide in the silicon waveguide layer 130 has a width of 50nm to 50 μm and a thickness of 50nm to 50 μm.
In order to solve the problem that the light transmission loss is large due to the fact that BCB resin is used as an adhesive layer in the prior art, the adhesive layer is replaced by the coating isolation layer 140 in the embodiment of the application. The encapsulating insulating layer 140 is made of silicon dioxide or silicon nitride.
In the embodiment of the present application, the functional thin film layer 150 is bonded to the clad separation layer 140 by using an ion implantation method and a bonding separation method, or by using a bonding method and a polishing method. Bonding refers to the bonding process that is performed without an intermediate layer and an external force field by bringing two materials to be bonded together. The Si-O structure in the silicon dioxide, or the Si-N structure in the silicon nitride, is a hydrophilic structure, and is easily combined with-OH, and a weak bond based on physical force is formed at the contact surface of the two materials to be bonded, thereby bonding the coating isolation layer 140 and the functional thin film layer 150 together.
In one realizable manner, preparing a silicon-on-insulator structure, which is a silicon substrate layer, a silicon dioxide layer and a top silicon layer in sequence from bottom to top; wherein the silicon substrate layer 110 and the silicon dioxide layer 120 may be obtained from a silicon-on-insulator (SOI) structure. Etching the top silicon layer 100 by using a dry etching method to form a silicon waveguide layer 130, wherein a groove structure is formed in the silicon waveguide layer 130 after etching, a layer of silicon dioxide or silicon nitride is deposited in the groove structure, the deposited silicon dioxide or silicon nitride fills the gap of the ridge waveguide and covers the silicon waveguide layer 130, and thus a cladding isolation layer 140 is formed; the thickness of the coating isolation layer 140 is 2-5 μm; the flatness of the coating isolation layer 140 is less than 1nm, and the roughness is less than 0.5 nm;
the coated barrier layer is comprised of a first coated barrier layer 1401 and a second coated barrier layer 1402;
the first coating isolation layer 1401 is positioned above the silicon waveguide layer and has the thickness of 20nm-2000 nm; the second coating isolation layer 1402 is arranged in the silicon waveguide layer and is flush with the silicon waveguide layer, and the thickness of the second coating isolation layer 1402 is equal to that of the silicon substrate waveguide layer;
the first and second encapsulating barrier layers 1401, 1402 are integrally formed.
Therefore, the bottom of the cladding isolation layer 140 in the embodiment of the present application extends to the bottom of the silicon waveguide layer 130, and the silicon waveguide layer 130 is embedded in the cladding isolation layer 140, that is, the thickness of the cladding isolation layer 140 is slightly greater than the thickness of the silicon waveguide layer 130. The thickness of the cladding spacer layer 140 is a thickness extending from the surface to the bottom of the silicon waveguide layer 130. The size of the light spot is typically several hundred nanometers to several micrometers, and is distributed between the silicon waveguide layer 130 and the functional thin film layer 150, and the cladding isolation layer 140 is typically thin, and thus does not affect the light propagation.
Because the material used by the cladding isolation layer 140 is silicon dioxide or silicon nitride, and the cladding isolation layer 140 can be tightly combined with the silicon waveguide layer 130, the surface can be planarized by adopting a CMP process to improve the roughness of the surface of the cladding isolation layer 140, so that the surface roughness is less than 0.5mm, the flatness is less than 1mm, the bonding with the functional thin film layer 150 can be facilitated, and the optical signal can be well coupled between the functional thin film layer 150 and the silicon waveguide layer 130. The surface of the coating isolation layer 140 according to the embodiment of the present application is a surface close to the functional film layer 150.
In this embodiment, since the waveguide grooves exist between the ridge-shaped and strip-shaped silicon waveguides, which may include a plurality of uniformly distributed ridges, and the waveguide grooves (groove structures) exist between the ridge-shaped and strip-shaped silicon waveguides, the height of the cladding isolation layer 140 at the ridge-shaped waveguide is higher than that at the waveguide grooves, when the cladding isolation layer 140 is deposited, if a single polishing process is adopted, as shown in fig. 3, the application adopts multiple polishing, and the deposition and polishing processes are repeated after each polishing, so as to achieve the purpose of flattening the cladding isolation layer 140, and finally, the material deposited at the waveguide grooves is the second cladding isolation layer 1402, and is integrally formed with the finally formed first cladding isolation layer 1401, so as to improve the coupling effect between the functional thin film layer 150 and the silicon waveguide layer 130.
The functional thin film layer 150 is an electro-optic crystal material for modulating an optical signal. Since light is transmitted in a material having a large refractive index, the refractive index of the cladding isolation layer 140 according to the embodiment of the present application is lower than that of the functional thin film layer 150, and the thickness of the functional thin film layer 150 is 50 to 3000nm or 400nm to 100 μm.
In this embodiment, the material of the functional thin film layer 150 may be selected according to the actual function to be realized, and the functional thin film layer 150 is selected from lithium niobate, lithium tantalate, and KTP (potassium titanyl phosphate, whose molecular formula is KTiOPO)4) And RTP (rubidium titanyl phosphate, molecular formula RbTiOPO)4) One of。
According to the technical scheme, the electro-optic crystal film provided by the application adopts the coating isolation layer to replace an adhesive layer in the prior art, and on one hand, the coating isolation layer can be subjected to planarization treatment, so that the surface roughness of one side close to the functional film layer is reduced, the diffuse reflection can be reduced, and the optical transmission loss is reduced; on the other hand, in the prior art, the BCB resin is used as the adhesive, the adhesive is filled between the two mutually contacted bonding surfaces, in the bonding process, the solvent in the adhesive volatilizes to generate bubbles, and the solvent in the middle volatilizes slowly, and the solvent at the edge volatilizes quickly, so that the bubbles are easily generated in the middle of the bonding surfaces, and the uniformity and the firmness of the functional film layer are poor. The coating isolation layer and the functional thin film layer are combined in a bonding mode, and uniformity and integrity of the functional thin film layer are guaranteed.
In the embodiment of the application, the SOI wafer structure is 50nm-50 mu mSi/50nm-5 mu mSiO from top to bottom2and/Si, if the etching depth of the top layer silicon is equal to the thickness of the top layer silicon, namely, in the case of complete etching, the SOI wafer subjected to the etching treatment forms a three-layer structure of a silicon substrate layer 110, a silicon dioxide layer 120 and a silicon waveguide layer 130. Since the requirement of the complete etching on the process is high, the over-etching is easy to occur, and once the silicon dioxide layer is etched, the planarization effect of the silicon waveguide layer is affected, in another embodiment, referring to the schematic structural diagram shown in fig. 2, the etching depth is smaller than the thickness of the top silicon layer by using the process of the incomplete etching, so that the silicon connection layer 160 is formed between the silicon waveguide layer 130 and the silicon dioxide layer 120. The incomplete etching method enables the etching depth of the silicon waveguide layer 130 to be adjusted and controlled within a certain range, and the transmission performance of light can be adjusted and controlled when the etching depth is different, namely, the thickness of the silicon waveguide layer is different. In addition, the strength of the top silicon layer is reduced after etching the top silicon layer into a silicon waveguide layer, and the silicon connection layer 160 can improve the strength after etching.
Based on the electro-optical crystal thin film disclosed above, the embodiment of the application further discloses an electro-optical modulator, which includes the electro-optical crystal thin film.
The embodiment of the application also provides a preparation method of the electro-optic crystal thin film, as shown in fig. 4, fig. 4 is a schematic structural diagram of the preparation process of the electro-optic crystal thin film.
Specifically, as shown in fig. 5, the preparation method comprises the following steps:
In the present application, the SOI structure is also referred to as an SOI wafer, and a 4-inch SOI wafer structure can be selected, where the SOI wafer structure is from top to bottom: 50nm-50 mu mSi/50nm-5 mu mSiO2Si, etching the top silicon layer by adopting a dry etching method to form ridge-shaped strip waveguides; wherein the top layer silicon is completely etched or partially etched.
If the complete etching is adopted, the processed SOI wafer structure sequentially comprises a silicon substrate layer, a silicon dioxide layer and a silicon waveguide layer from top to bottom; if the incomplete etching is adopted, the processed SOI wafer structure sequentially comprises a silicon substrate layer, a silicon dioxide layer, a silicon connecting layer and a silicon waveguide layer from bottom to top.
And 2, filling a coating isolation layer in the groove structure, and flattening the coating isolation layer.
The method for preparing the cladding isolation layer is not particularly limited, and the method for preparing the cladding isolation layer on the silicon waveguide layer includes, but is not limited to: deposition, magnetron sputtering, evaporation or electroplating, and the polishing method can adopt CMP.
Depositing a coating isolation layer in a groove structure formed on a silicon waveguide surface, filling the groove structure with the coating isolation layer, covering the silicon waveguide layer, polishing the coating isolation layer until the silicon waveguide layer is polished, stopping polishing when the polishing removal rate is almost zero, and repeating the step for at least three times; wherein the final polishing leaves a cladding isolation layer of a target thickness (e.g., 50nm, 100nm, 500nm, 1000nm, 2000nm, etc.) over the silicon waveguide layer until the roughness of the cladding isolation layer is less than 0.5nm and the surface flatness is less than 1 nm.
And 3, preparing a functional thin film layer with a target thickness on the coating isolation layer to obtain the electro-optic crystal thin film.
In this step, the preparation method of the functional thin film layer may select an ion implantation method and a bonding separation method, and may also select a bonding method and a grinding and polishing method, which is not specifically limited in this application.
When the ion implantation method and the bonding separation method are selected to be used, the scheme comprises the following steps: performing ion implantation on the functional film, wherein the implantation energy of the ion implantation is 50-1000KeV, and the dosage is 1E16-1E17ions/cm2Forming a functional thin film wafer with a three-layer structure of a thin film layer, a separation layer and a residual material layer; preparing and forming a bonding body by adopting a plasma bonding mode; under vacuum environment or under protective atmosphere formed by at least one of nitrogen and inert gas; wherein the heat preservation temperature is 100-600 ℃, and the heat preservation time is 1 min-48 h until the residual material layer is separated from the bonding body to form the lithium niobate single crystal film; polishing the lithium niobate single crystal film to 50-3000nm (such as 100nm, 400nm, 500nm, 800nm, 1000nm, 2000nm, etc.) to obtain the electro-optic crystal film with nanometer-level thickness.
When the bonding method and the grinding and polishing method are selected to be used, the scheme comprises the following steps: preparing and forming a bonding body by adopting a plasma bonding mode; under vacuum environment or under protective atmosphere formed by at least one of nitrogen and inert gas; wherein the heat preservation temperature is 100-600 ℃, and the heat preservation time is 1 min-48 h; thinning the film to 1-102 μm by mechanical grinding, and polishing to 400nm-100 μm (such as 500nm, 1 μm, 5 μm, 10 μm, 50 μm, etc.), to obtain the lithium niobate single crystal film with micron-scale thickness.
The purpose of the bonding body heat preservation is to improve the bonding force of the bonding body to be more than 10 MPa.
The thickness of the thin film layer can be adjusted by adjusting the ion implantation depth, and specifically, the larger the ion implantation depth is, the larger the thickness of the prepared thin film layer is; conversely, the smaller the depth of ion implantation, the smaller the thickness of the thin film layer produced.
After ion implantation and before bonding, it is usually necessary to clean the two contacting bonding surfaces to enhance the bonding effect.
In the application, different activation means are selected according to the thickness of the selected electro-optic crystal material. Since the thickness of the ion implantation is limited, it is not suitable for electro-optic crystal materials with a relatively large thickness. When the thickness of the selected electro-optic crystal material is thicker, ion implantation is not carried out, and direct bonding is carried out.
According to the preparation method disclosed by the embodiment of the application, the preparation method of the electro-optic crystal film disclosed by the embodiment of the application is simple in process, easy to operate and suitable for large-scale popularization and application.
The embodiment of the application also provides an electro-optical modulator which comprises the electro-optical crystal film prepared by the preparation method provided by any one of the possible implementation modes of the embodiment.
Examples
Example 1
(1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nmSi/2 μmSiO from the top down2and/Si. And etching the top silicon of the SOI wafer by using a dry etching method, completely etching the top SI, etching a ridge-shaped strip waveguide, wherein the size of the ridge-shaped strip waveguide is 1 mu m in width and 220nm in thickness, forming a groove structure in the silicon waveguide layer after etching, and the height of the groove structure is the thickness of the ridge-shaped strip waveguide.
(2) Cleaning the etched ridge-type strip waveguide surface of the SOI wafer, and depositing a layer of SiO 2.5 mu m on the ridge-type silicon waveguide surface by adopting PECVD2And filling the groove structure and covering the silicon waveguide layer to form a coating isolation layer.
(3) For SiO covered ridge waveguide in step (2)2Planarizing by CMP process, repeating PECVD to deposit silicon dioxide, and polishing for 3 timesAnd finally, the cladding isolation layer with the thickness of 1000nm is reserved above the silicon waveguide layer by polishing for the first time, and the roughness of the surface of the cladding isolation layer is finally improved, so that the surface roughness is less than 0.5nm, and the surface flatness is less than 1 nm.
(4) Preparing a lithium niobate wafer having a size of 4 inches, and implanting helium ions (He) by ion implantation+) Implanting helium ions into the lithium niobate wafer at an implantation energy of 200KeV and a dose of 4E16ions/cm2And forming the lithium niobate wafer with a three-layer structure of a thin film layer, a separation layer and a residual material layer.
(5) And (4) cleaning the coating isolation layer in the step (3) and the thin film layer in the step (4), and bonding the thin film layer of the cleaned lithium niobate wafer and the coating isolation layer in the step (3) by adopting a plasma bonding method to form a bonded body.
(6) And (3) putting the bonding body into heating equipment, and preserving heat at high temperature until the residual material layer is separated from the bonding body to form the lithium niobate single crystal film. The heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa, and the damage of ion implantation to the thin film layer can be recovered, so that the obtained lithium niobate thin film layer has the property close to that of a lithium niobate wafer.
(7) Polishing and thinning the lithium niobate single crystal film to 400nm to obtain the lithium niobate single crystal film with the nanoscale thickness.
It can be seen that example 1 is a method using ion implantation + bonding separation, in which the top silicon is completely etched through and the cladding isolation layer is SiO2The functional film layer is prepared by bonding and separating the functional film layer and the coating isolation layer after ion implantation. The lithium niobate single crystal film with the nanometer-level thickness can be obtained.
Example 2
(1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nmSi/2 μmSiO from the top down2and/Si. Using dry etching to the top layer Si of the SOI waferAnd etching by a method, wherein the top layer SI is completely etched through to form a ridge-shaped strip waveguide, the dimension of the ridge-shaped strip waveguide is 1 μm in width and 220nm in thickness, a groove structure is formed in the silicon substrate groove waveguide layer after etching, and the height of the groove structure is the thickness of the ridge-shaped waveguide.
(2) Cleaning the etched ridge-type strip waveguide surface of the SOI wafer, and depositing a layer of SiO 2.5 mu m on the ridge-type silicon waveguide surface by adopting PECVD2And filling the groove structure and covering the silicon waveguide layer to form a coating isolation layer.
(3) SiO for covering the ridge-shaped silicon waveguide in the step (2)2And flattening by adopting a CMP (chemical mechanical polishing) process, repeatedly carrying out PECVD (plasma enhanced chemical vapor deposition) to deposit silicon dioxide, then polishing for 3 times, retaining a coating isolation layer with the thickness of 2000nm above the silicon substrate groove waveguide layer in the last polishing, and finally improving the roughness of the surface of the coating isolation layer to ensure that the surface roughness is less than 0.5nm and the surface flatness is less than 1 nm.
(4) Preparing a lithium niobate wafer with the size of 4 inches, cleaning a process surface, and bonding the process surface of the cleaned lithium niobate wafer and a silicon dioxide surface (a coating isolation layer) of an SOI substrate by adopting a plasma bonding method to form a bonding body.
(5) And (3) putting the bonding body into heating equipment, and carrying out heat preservation at high temperature, wherein the heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one of nitrogen and inert gas, the heat preservation temperature is 400 ℃, the heat preservation time is 3 hours, and the bonding force can be improved to be more than 10 MPa.
(6) And thinning the lithium niobate single crystal film to 22 mu m by adopting a mechanical grinding mode, and then polishing to 20 mu m to obtain the lithium niobate single crystal film with micron-sized thickness.
Example 3
(1) Preparation rulerAn SOI wafer 4 inches in size, 0.5mm thick and having a smooth surface, the SOI wafer having a structure of 220nmSi/2 μmSiO from top to bottom2and/Si. And etching the top layer Si of the SOI wafer by using a dry etching method to etch a ridge-type strip waveguide, wherein the size of the ridge-type strip waveguide is 1 mu m × 160nm in width, the thickness of the reserved silicon connecting layer is 60nm, a groove structure is formed in the silicon waveguide layer after etching, and the height of the groove structure is the thickness of the ridge-type strip waveguide.
(2) And cleaning the etched ridge type silicon waveguide surface of the SOI wafer, and adopting PECVD (depositing a layer of 2.5 mu m silicon nitride on the ridge type silicon waveguide surface, filling the groove structure, and covering the silicon waveguide layer to form a coating isolation layer.
(3) And (3) flattening the silicon nitride covered with the ridge-shaped silicon waveguide in the step (2) by adopting a CMP (chemical mechanical polishing) process, repeating PECVD (plasma enhanced chemical vapor deposition) to deposit silicon dioxide, then polishing, repeating the process for 3 times, retaining a coating isolation layer with the thickness of 1000nm above the silicon waveguide layer in the last polishing, and finally improving the roughness of the surface of the coating isolation layer to ensure that the surface roughness is less than 0.5nm and the surface flatness is less than 1 nm.
(4) Preparing a lithium niobate wafer having a size of 4 inches, and implanting helium ions (He) by ion implantation+) Implanting helium ions into the lithium niobate wafer at an implantation energy of 200KeV and a dose of 4E16ions/cm2And forming the lithium niobate wafer with a three-layer structure of a thin film layer, a separation layer and a residual material layer.
(5) And (3) cleaning the isolation layer coated in the step (3) and the thin film layer coated in the step (4), and bonding the thin film layer of the cleaned lithium niobate wafer and the silicon nitride surface of the SOI substrate by adopting a plasma bonding method to form a bonded body.
(6) And (3) putting the bonding body into heating equipment, and preserving heat at high temperature until the residual material layer is separated from the bonding body to form the lithium niobate single crystal film. The heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa, and the damage of ion implantation to the thin film layer can be recovered, so that the obtained lithium niobate thin film layer has the property close to that of a lithium niobate wafer.
(7) Polishing and thinning the lithium niobate single crystal film to 400nm to obtain the lithium niobate single crystal film with the nanoscale thickness.
It can be seen that, in example 3, a method of ion implantation and bonding separation is adopted, in which the top silicon is not completely etched, the coating isolation layer is silicon nitride, the functional thin film layer is lithium niobate, and the functional thin film layer is obtained by bonding and separating the functional thin film layer and the coating isolation layer after ion implantation. The lithium niobate single crystal film with the nanometer-level thickness can be obtained.
Example 4
(1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nmSi/2 μmSiO from the top down2and/Si. And etching the top layer Si of the SOI wafer to form ridge-shaped strip waveguides by using a dry etching method, wherein the dimension of the ridge-shaped strip waveguides is 1 mu m in width and 160nm in thickness, the thickness of the reserved silicon connecting layer is 60nm, and groove structures are formed in the silicon substrate groove waveguide layer after etching, and the height of each groove structure is equal to the thickness of the ridge-shaped waveguides.
(2) And cleaning the etched ridge type strip waveguide surface of the SOI wafer, depositing a layer of 2.5 mu m silicon nitride on the ridge type silicon waveguide surface by adopting PECVD (plasma enhanced chemical vapor deposition), filling the groove structure, and covering the silicon waveguide layer to form a coating isolation layer.
(3) And (3) flattening the silicon nitride covered with the ridge-shaped silicon waveguide in the step (2) by adopting a CMP (chemical mechanical polishing) process, repeating PECVD (plasma enhanced chemical vapor deposition) to deposit silicon dioxide, then polishing, repeating the process for 3 times, reserving a cladding isolation layer with the thickness of 1000nm above the silicon substrate groove waveguide layer in the last polishing, and finally improving the roughness of the surface of the cladding isolation layer to ensure that the surface roughness is less than 0.5nm and the surface flatness is less than 1 nm.
(4) Preparing a lithium niobate wafer with the size of 4 inches, cleaning the process surface, and bonding the process surface of the cleaned lithium niobate wafer with the silicon nitride surface of the SOI substrate by adopting a plasma bonding method to form a bonded body.
(5) And (3) putting the bonding body into heating equipment, and carrying out heat preservation at high temperature, wherein the heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one of nitrogen and inert gas, the heat preservation temperature is 400 ℃, the heat preservation time is 3 hours, and the bonding force can be improved to be more than 10 MPa.
(6) And thinning the lithium niobate single crystal film to 22 mu m by adopting a mechanical grinding mode, and then polishing to 20 mu m to obtain the lithium niobate single crystal film with micron-sized thickness.
Embodiment 4 is a method of direct bonding and polishing, in which the top silicon is not completely etched, the coating isolation layer is silicon nitride, the functional thin film layer is lithium niobate, the functional thin film layer is directly bonded to the coating isolation layer, and then the top silicon is polished. Obtaining the lithium niobate single crystal film with micron-sized thickness.
In addition, on the basis of the above embodiments, other embodiments may also be derived, such as: on the basis of each embodiment, the functional thin film layer in the embodiment is replaced by lithium tantalate, KTP or RTP, and other process parameters can be changed without changing or according to needs; that is, one skilled in the art can combine alternative materials and process parameters according to the above embodiments, and the application is not limited specifically.
The present application has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the presently disclosed embodiments and implementations thereof without departing from the spirit and scope of the present disclosure, and these fall within the scope of the present disclosure. The protection scope of this application is subject to the appended claims.
Claims (12)
1. An electro-optic crystal film characterized in that,
the electro-optic crystal film sequentially comprises the following components from bottom to top: the silicon substrate layer (110), the silicon dioxide layer (120), the silicon waveguide layer (130), the cladding isolation layer (140) and the functional thin film layer (150); the silicon waveguide layer (130) is embedded in the cladding isolation layer (140);
the refractive index of the coating isolation layer (140) is lower than that of the functional thin film layer (150), and the coating isolation layer (140) is subjected to planarization treatment and can be bonded with the functional thin film layer (150).
2. The electro-optic crystal film of claim 1, wherein the functional thin film layer (150) is selected from one of lithium niobate, lithium tantalate, KTP, and RTP, and the functional thin film layer (150) has a thickness of 50-3000nm or 400nm-100 μm.
3. The electro-optic crystal film of claim 1, wherein the encapsulating spacer layer (140) is silicon dioxide or silicon nitride, the encapsulating spacer layer (140) having a flatness of less than 1nm and a roughness of less than 0.5 nm;
the coated insulating layer (140) is composed of a first coated insulating layer (1401) and a second coated insulating layer (1402);
the first coating isolation layer (1401) is positioned above the silicon waveguide layer and has the thickness of 20nm-2000 nm; the second coating isolation layer (1402) is arranged in the silicon waveguide layer and is flush with the silicon waveguide layer, and the thickness of the second coating isolation layer (1402) is equal to that of the silicon waveguide;
the first and second encapsulating barrier layers (1401, 1402) are integrally formed.
4. The electro-optic crystal film of claim 1, wherein the silicon waveguide layer (130) is in the shape of a ridge stripe structure, and the width of the ridge waveguide in the silicon waveguide layer (130) is 50nm-50 μm and the thickness is 50nm-50 μm.
5. The electro-optic crystal film of any of claims 1-4, further comprising a silicon connection layer (160), the silicon connection layer (160) being located between the silicon dioxide layer (120) and the silicon waveguide layer (130);
the sum of the thicknesses of the silicon connection layer (160) and the silicon waveguide layer (130) is 50nm-50 μm, and the thickness of the silicon dioxide layer (120) is 50nm-5 μm.
6. An electro-optic modulator comprising the electro-optic crystal film of any one of claims 1-5.
7. A method for preparing an electro-optic crystal film, comprising:
preparing a silicon-on-insulator structure, and etching the top silicon of the silicon-on-insulator structure to form a silicon waveguide layer; the silicon-on-insulator structure sequentially comprises a silicon substrate layer, a silicon dioxide layer and top silicon from bottom to top; forming a groove structure in the silicon waveguide layer after etching;
filling a coating isolation layer in the groove structure, and flattening the coating isolation layer;
and preparing a functional thin film layer with a target thickness on the coating isolation layer to obtain the electro-optic crystal thin film.
8. The production method according to claim 7,
etching the top silicon of the silicon-on-insulator structure, comprising: etching the top silicon layer by a dry etching method to form a ridge-shaped strip-shaped silicon waveguide; wherein the top layer silicon is completely etched or partially etched.
9. The method according to claim 7, wherein the filling of the trench structure with a cladding isolation layer and the planarization of the cladding isolation layer comprise:
filling a coating isolation layer in the groove structure, filling the groove structure with the coating isolation layer, covering the silicon waveguide layer, and polishing the coating isolation layer, wherein the step is repeated for at least three times;
and finally, the coating isolation layer with the target thickness is reserved above the silicon waveguide layer through polishing, the roughness of the coating isolation layer is less than 0.5nm, and the surface flatness is less than 1 nm.
10. A method of fabricating a cladding spacer layer on a silicon waveguide layer according to claim 9, comprising: deposition, magnetron sputtering, evaporation or electroplating.
11. The production method according to claim 7, wherein a functional thin film layer is produced on the clad separator layer by an ion implantation method and a bonding separation method, or by a bonding method and a lapping polishing method.
12. An electro-optical modulator comprising the electro-optical crystal film produced by the production method according to any one of claims 7 to 11.
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